Question

Calculate the exact masses and relative isotopic abundances of all the isotopomers of dichloromethane. Consider only the two most abundant isotopes of carbon and chlorine, and ignore deuterium and tritium (i.e., assume the natural abundance of 1H is 1.000000). Summarize your results by giving in a table the empirical formula for each isotopomer with superscripted atomic masses, the nominal m/z and the exact m/z values for each in a table .

To calculate natural abundance, make a product of the natural abundance of each element raised to the power of the number of times it occurs in the molecule. Then multiply it by the number of distinguishable ways that you can make this isotopomer, if the nuclei are labelled. For example, for two C nuclei labelled A and B, there is only one way to make 13C-13C (13CA13CB) but there are two ways to make 12C-13C (i.e., 13CA12CB and 12CA13CB). When you’re done correctly, all the abundances should add up to 100%, so you can use this to check for errors.

Answer 1

Molecular Formula	Nominal Mass	Exact Mass	Population
12CH235Cl2	84	83.938	56.749
13CH235Cl2	85	84.941	0.631
12CH235Cl37Cl	86	85.935	36.335
13CH235Cl37Cl	87	86.938	0.404
12CH237Cl2	88	87.932	5.816
13CH237Cl2	89	88.935	0.065

Atomic mass used for exact m/z:

12C=12.0000	13C=13.0034
35Cl=34.96885	37Cl=36.9659

Below see the working principle